1. Field of the Invention
The present invention is concerned with a new process for preparing 4-hydroxy-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxides, starting with amide-substituted-2,3-dihydro-3-oxo-1,2-benzisothiazole-2-acetamide 1,1-dioxides.
2. Description of the Prior Art
The preparation of certain 4-hydroxy-2H-1,2-benzothiazine-3-carboxamides by the rearrangement of specific saccharin derivatives is known. For example, Lombardino, in U.S. Pat. No. 3,591,584, and in J. Med. Chem. 14:1171-1175 (1971), discloses the use of saccharin acetic acid esters (3-oxo-1,2-benzisothiazoline-2-acetic acid methyl ester) to prepare 3,4-dihydro-4-oxo-1,2-benzothiazine-3-carboxylate 1,1-dioxide esters which are then alkylated on the 2-position and further treated with an amine to obtain the corresponding carboxamides. The use of a similar method to prepare 4-hydroxy-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxide is described by Rasmussen in U.S. Pat. No. 3,501,466.
Zinnes, et al., describe a similar reaction starting with the analogous methyl ketone, in J. Org. Chem. 30:2241-2246 (1975).
Fabian, et al., in U.S. Ser. No. 577,567, now U.S. Pat. No. 3,987,038, filed May 21, 1975, and in U.S. Ser. No. 577,568, filed May 21, 1975, now U.S. Pat. No. 3,957,772, disclose the rearrangement of 2,3-dihydro-N-(5-methyl-3-isoxazolyl)-3-oxo-1,2-benzisothiazole-2-acetamid e 1,1-dioxide to 1-{ 5-(4-hydroxy-2H-1,2-benzothiazin-3-yl)-1,2,4-oxadiazol-3-yl!methyl} ethanone S,S-dioxide which upon methylation and further treatment, undergoes a second rearrangement to form 4-hydroxy-3-(5-methyl-3-isoxazolylcarbamoyl)-2-methyl-2H-1,2-benzothiazine 1,1-dioxide.